Multi-point pyrometry with real-time surface emissivity compensation

ABSTRACT

A multi-point non-invasive, real-time pyrometry-based temperature sensor (200) for simultaneously sensing semiconductor wafer (22) temperature and compensating for wafer emissivity effects. The pyrometer (200) measures the radiant energy that a heated semiconductor wafer (22) emits and coherent beams of light (224) that the semiconductor wafer (22) reflects. As a result, the sensor (200) generates accurate, high-resolution multi-point measurements of semiconductor wafer (22) temperature during a device fabrication process. The pyrometer (200) includes an infrared laser source (202) that directs coherent light beam (203) into beam splitter (204). From the beam splitter (204), the coherent light beam (203) is split into numerous incident coherent beams (210). Beams (210) travel via optical fiber bundles (218) to the surface of semiconductor wafer (22) within the fabrication reactor (80). Each optical fiber bundle (218) collects reflected coherent light beam and radiant energy from wafer (22). Reflected coherent light beam (226) and radiant energy (222) is directed to a detector (240) for detecting signals and recording radiance, emissivity, and temperature values. Multiple optical fiber bundles (218) may be used in the sensor (200) for high spatial resolution multi-point measurements of wafer (22) temperature for precision real-time process control and uniformity optimizations.

NOTICE: THE U.S. GOVERNMENT HAS A PAID-UP LICENSE IN THIS INVENTION ANDTHE RIGHT IN LIMITED CIRCUMSTANCES TO REQUIRE THE PATENT OWNER TOLICENSE OTHERS ON REASONABLE TERMS AS PROVIDED FOR BY THE TERMS OF THECONTRACT BETWEEN ASSIGNEE AND THE UNITED STATES AIR FORCE UNDER THEPROGRAM NAME MMST.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to measurement of semiconductorwafer physical characteristics, and more particularly to a method andapparatus for semiconductor wafer temperature measurements based onmulti-point pyrometry with noninvasive real-time surface emissivitymeasurement and compensation.

BACKGROUND OF THE INVENTION

Integrated circuit chip manufacturers fabricate semiconductor devices bydifferent combinations of processes. One widely used processingtechnique is chemical-vapor deposition (CVD) which is employed to formvarious material layers (metals, dielectrics, semiconductors) on thesurface of semiconductor wafers. The material layers which manufacturersapply and etch may comprise various dielectric or insulating layers inaddition to one or more of the following conductive layers: a thin metalcoating such as tungsten, aluminum, copper, or gold; a thin polysiliconcoating doped with conductive impurities; or other layers of metalsilicides and metal nitrides. Process control and manufacturingtolerances apply to the sequential device fabrication processes.Deviations from specified target tolerances in excess of only a fewpercentage points during various device fabrication processes may resultin defective and rejected semiconductor chips.

In thermal processing equipment such as in a single-wafer rapid thermalprocessing (RTP) reactor, one of the critical process parameters is thewafer temperature. Therefore, it is important to measure the wafertemperature and its distribution uniformity in real-time by anon-invasive temperature sensing device. Repeatable, precise, andprocess-independent measurements of the wafer temperature are among themost important requirements of semiconductor processing equipment (suchas RTP) in integrated circuit manufacturing.

FIGURE shows an RTP reactor 20 containing a semiconductor wafer 22 andin which a typical non-contact temperature measuring pyrometer 24detects radiance or black-body radiation emitted from the heated wafer.RTP reactor 20 has a process environment bounded by quartz (or metallic)process chamber (consisting of transparent walls 32, 36) containedwithin casing with a lower wall 28 and upper wall 40. Within RTP reactor20 wafer 22 is heated on both sides by two banks of linear heating lamps(tungsten-halogen lamps) 30 and 38 through optical windows 32 and 36.The RTP system may employ only one bank of tungsten-halogen lamps forone-sided wafer heating. Thermocouple 34 may be used to provide wafertemperature measurement for calibration of the pyrometry readings. Sincethermocouple requires wafer contact, it is not used during actual deviceprocessing.

Optical pyrometry has been used as a non-invasive method for wafertemperature measurement in the known RTP systems. However, the accuracyand reproducibility of conventional pyrometry are very sensitive to thewafer bulk and surface optical properties (or emissivity), interferencedue to the heating lamps, process environment, and the type of processbeing performed in the reactor. With the double-sided lamp heatingarrangement, the pyrometer will usually experience direct radiationexposure from the lamps regardless of the positioning of the pyrometer.However, the disturbance of the pyrometer reading will be minimal if thespectral distribution of the heating lamps has no overlap with thepyrometer's operating spectral band or wavelength.

With the single-sided lamp heating (example shown with a single arclamp) arrangement of FIG. 2 shown with a metallic process chamber, ahole 53 can be formed through a side of the RTP vacuum chamber 50opposite the heat lamp 66 in order to insert an optical window (thesingle-sided RTP system 50 may use one bank of tungsten-halogen lampsinstead of a single high-power arc lamp). Pyrometer 52 is placed nearthe hole 53 to detect a portion of the emitted black-body radiation 54from wafer 22. This arrangement may be somewhat more suitable than theabove-mentioned double heat lamp arrangement since it is free (notcompletely) from direct viewing of the lamp and its interferenceeffects. However, silicon wafer 22 may remain at least partiallytransparent to the lamp radiation in the infrared region (e.g., beyond1.5 μm) at lower wafer temperatures (e.g., below 600° C.), so pyrometer52 may still be affected by lamp radiation passed through a partiallytransparent wafer 22.

Conventional pyrometry techniques also assume a semiconductor wafer hasa known fixed emissivity. In actuality, emissivity can change fromsemiconductor wafer to semiconductor wafer. Emissivity values depend onvarious layers of materials present on the semiconductor wafer,substrate background doping, semiconductor wafer backside surfaceroughness, and semiconductor wafer temperature. The presence of devicepatterns on the semiconductor wafer and the pyrometry wavelength mayalso affect spectral emissivity. In practice, while the amount of errorthat using an erroneous value for wafer emissivity can produce isusually uncertain, it has been shown to cause wafer temperaturemeasurement errors up to 10's or even 100's of ° C.

FIG. 3 is a graph of silicon wafer emissivity as a function ofwavelength. For different wafer temperatures [in ° K], FIG. 3 showsmeasured emissivity for a 1.77 mm thick silicon wafer with a relativelylow level of n-type doping. The substrate is a comparatively pure samplehaving a resistivity of 1.4 Ω-cm. All measurements in FIG. 3 were madeat a vacuum of 10⁻⁴ mm Hg. The plot of FIG. 3 shows measurements ofspectral emissivity for silicon from 0.4 to 15.0 μm at temperaturesranging from 543° K. to 1070° K. Thermal radiation of silicon is due toband-to-band transitions, free carriers and lattice vibrations. Thisradiation lies primarily in the visible and infrared regions of thespectrum. FIG. 3 shows that spectral emissivity changes significantlyfor pyrometry applications as a function of wavelength. As temperaturechanges, emissivity will change. Thus, it is not possible to accuratelymeasure temperature of the semiconductor wafer using pyrometry, unlessthe pyrometry-based techniques compensate for changes in emissivity as afunction of changes in temperature or surface optical conditions.

FIG. 4 illustrates the calculated relationship between the backsidespectral 5.4 μm emissivity and polysilicon layer thickness for asemiconductor substrate with two backside films and a bare front side.For a 500 μm thick silicon substrate with a resistivity of 5 Ω-cm at900° K. with two material layers on the backside, FIG. 4 shows thespectral backside emissivity vs. polysilicon film thickness for variousoxide layer thicknesses. For example, with a 100 Å silicon dioxide firstlayer, the shows emissivity to be approximately 0.7 uniformly aspolysilicon thickness increases from 0 to 1000 nm. With increasedbackside silicon dioxide layer thickness, emissivity will changesignificantly as a function of polysilicon layer thickness. In theextreme case shown, with a 5,000 Å backside silicon dioxide, FIG. 4(graph 72) shows that emissivity can range from 1.0 to approximately0.25 with widely varying values therebetween. These emissivityvariations can cause significant temperature measurement errors inconventional pyrometry.

Thus, there is a need for an improved and reliable method and apparatusto precisely measure the temperature of a wafer in a semiconductordevice fabrication reactor.

Thus, there is a need for a method and apparatus to provide real-timein-situ non-invasive temperature measurements of semiconductor wafersduring device fabrication processes.

SUMMARY OF THE INVENTION

The present invention accordingly provides an apparatus and method formulti-point real-time non-invasive in-situ semiconductor wafertemperature measurements with real-time emissivity compensation thatsubstantially eliminates and reduces disadvantages and limitationsassociated with prior semiconductor wafer pyrometry-based temperaturemeasurement methods, apparatuses, and systems.

The sensor of the present invention is an improved multi-pointnon-invasive, real-time pyrometry for simultaneously sensingsemiconductor wafer radiance and measuring wafer emissivity. Theimproved multi-point sensor measures the incoherent radiant energy orblack-body radiation that a semiconductor wafer generates when heated.The incoherent radiant energy that the pyrometer senses is the waferblack-body radiation which depends both on temperature and emissivity ofthe wafer. For a specified spectral band and with a known waferemissivity, the wafer black-body radiation is a unique function of thewafer temperature. By simultaneously measuring the wafer radiance andemissivity, therefore, the sensor can determine the true wafertemperature. The sensor generates accurate, high-resolution multi-pointmeasurements of semiconductor wafer temperature during a devicefabrication process.

Associated with a semiconductor wafer fabrication reactor, the sensorincludes an infrared laser that directs a coherent beam of light into abeam splitter. From the beam splitter, the coherent laser beam is splitinto numerous coherent beams. These beams have approximately equalintensity, wavelength, coherence, and polarization. The beams travel byoptical fiber bundles to the surface of a semiconductor wafer within thefabrication reactor. Each of the optical fiber bundles directs thecoherent energy as an incident coherent beam to the wafer surface. Eachoptical fiber bundle also collects a reflected coherent beam that occursas a result of a fraction of the incident coherent beam being reflectedby the wafer. The optical fibers are also positioned proximate to thewafer for receiving incoherent radiant energy from the heated wafersurface.

The reflected coherent laser beam and incoherent radiant energy thateach optical fiber bundle collects is directed to a detector fordetecting and converting both optical signals. The reflected coherentbeam produces a real-time non-invasive measurement of semiconductorwafer emissivity for emissivity compensation. The incoherent radiantenergy measurement determines the semiconductor wafer radiance for whichreal-time emissivity compensation will occur. Multiple optical fibersare used in the sensor. This permits accurate, high-resolutiontemperature and emissivity measurements at various points on the waferfor precision process control and real-time uniformity optimizations.

A technical advantage of the present invention is that it allowsmulti-point temperature sensing with good spatial resolution to allowreal-time wafer temperature measurement for dynamic temperature andprocess uniformity control.

A further technical advantage of the present invention is that itovercomes measurement error caused by wafer emissivity variations aswell as surface roughness-related variations from wafer to wafer duringa series of semiconductor wafer fabrication processes.

Yet another technical advantage of the present inventions is that itprovides a method and sensor system that can be useful to preciselycontrol wafer temperature and its distribution uniformity during asemiconductor device fabrication process.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its modes of use and advantages are best understood byreference to the following description of illustrative embodiments whenread in conjunction with the accompanying drawings, wherein:

FIGS. 1 and 2 are examples of a prior art pyrometry devices used forsemiconductor wafer temperature measurements in rapid thermal processingequipment;

FIG. 3 is a graph of silicon wafer emissivity as a function ofwavelength for various temperatures;

FIG. 4 is a graph of backside wafer emissivity at a 5.4 μm as a functionof backside polysilicon and oxide layer thicknesses;

FIG. 5 is a schematic drawing of a single-wafer semiconductor devicefabrication reactor using the present invention;

FIG. 6 is a schematic drawing illustrating a preferred embodiment of thepresent invention;

FIG. 7 is a cross-sectional view of a time-division chopper multiplexerwith optical fiber interface used in a preferred embodiment of thepresent invention;

FIG. 8 is a schematic cross-sectional side view of a time-divisionchopper multiplexer with fiber interface used in a preferred embodimentof the present invention;

FIG. 9 is a top perspective view of the fiber adapter module of apreferred embodiment of the present invention;

FIG. 10 is a top perspective view of the chopper wheel used in apreferred embodiment of the present invention;

FIG. 11 is a time chart illustrating time-division chopping ofsemiconductor wafer radiance, reflectance, and transmissionmeasurements;

FIGS. 12a through 12f are various embodiments of fiber-optic bundlesusable with the present invention;

FIG. 13 is a cut-away side diagrammatic view of a cooling jacket for thefiber-optic bundles used in a preferred embodiment of the presentinvention;

FIG. 14 is a partially cut-away perspective view of the presentinvention integrated with the process control computer for the purposeof real-time semiconductor wafer fabrication process control;

FIG. 15 is a schematic block diagram of the integrated sensor system ofFIG. 14;

FIG. 16 is a plot of the parameter, 1-S_(r), versus semiconductor waferRMS surface roughness (S_(r) is the scattering parameter);

FIG. 17 is a diagram of calibration data relating the parameter,1-S_(r), obtained at a laser wavelength of 1.3 μm to scattering data ata wavelength of 5.4 μm; and

FIG. 18 is a flow chart illustrating use of the integrated sensor systemincorporating the preferred embodiment of the present invention togetherwith a process control computer for real-time semiconductor wafertemperature measurement and fabrication process control.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment of the present invention is best understood byreferring to the FIGUREs wherein like numerals are used for like andcorresponding parts of the various drawings.

Pending U.S. patent application Ser. No. 702,798 by Dr. Mehrdad M.Moslehi and Dr. Habib Najm entitled "Fiber-Optic Network for Multi-PointEmissivity-Compensated Semiconductor Wafer Pyrometry", filedsimultaneously with this application describes a method and apparatusthat utilizes a fiber-optic network for multi-point, noninvasive,in-situ, pyrometry-based semiconductor wafer temperature measurementswith real-time emissivity compensation. Pending U.S. patent applicationSer. No. 702,792 by Dr. Mehrdad M. Moslehi and Dr. Habib Najm entitled"Multi-Point Semiconductor Wafer Fabrication Process Temperature ControlSystem", filed simultaneously with this application describes a methodand system that integrates a sensor for multi-point, non-invasive,in-situ, pyrometry-based semiconductor wafer temperature measurementswith real-time emissivity compensation and a surface roughness sensordescribed more particularly in pending U.S. patent application Ser. No.07/638,472, filed Dec. 31, 1990 by Moslehi and entitled "Sensor forSemiconductor Device Manufacturing Process Control". The abovereferenced patent applications are incorporated herein in theirentirety.

FIG. 5 is a schematic representation of a semiconductor fabricationreactor 80 establishing a representative single-wafer environment of thepresent invention. Within a single-wafer rapid thermal/plasma processingreactor such as the Texas Instruments' automated vacuum processor (AVP),may reside a semiconductor wafer 22 for device processing. Beginning thebottom right hand corner of FIG. 5, gas distribution network 82 maycomprise two gas manifolds: a non-plasma process gas manifold (notshown) and a plasma manifold. Non-plasma process gas manifold connectsto a gas line 91 which penetrates through reactor casing 92 and processchamber wall 94 to proceed through ground electrode 96 and into gasinjector 100. Plasma manifold connects via gas line 89 into dischargecavity 88 for generating process plasma. Process plasma activatedspecies pass within plasma discharge tube 90 through reactor casing 92and process chamber wall 94, through ground electrode 96 and into waferprocess environment. Above gas injector assembly 100 and supported bylow thermal mass pins 104 appears semiconductor wafer 22. Low thermalmass pins 104 are supported by ground electrode 96 within processchamber 38. Process chamber 38 includes optical quartz window 106 whichseparates semiconductor wafer 22 from tungsten-halogen heating lampmodule 134. In the preferred embodiment of the present invention,tungsten halogen heating lamp module 134 includes multi-point sensor ofthe present invention which subsequent FIGUREs and associated textdescribe.

Process chamber 38 also includes pump down interface 120 which removesprocess gas and plasma into pumping package 122. Additionally, isolationgate 108 permits passage of semiconductor wafers 22 from the load-lockchamber 110 into process chamber 38. To permit movement of semiconductorwafers 22 into process chamber 38, process chamber wall 94 is supportedby vertically moving element (not shown). Within load-lock chamber 110appear a stack of semiconductor wafers 112 from which wafer handlingrobot 114 removes a single semiconductor wafer 22 for processing. In thepreferred embodiment of the present invention, load-lock chamber 110 mayalso include optical scattering module 116 described by pending U.S.patent application Ser. No. 07/638,472, filed Dec. 31, 1990 by Moslehiand entitled "Sensor for Semiconductor Device Manufacturing ProcessControl". That U.S. Patent Application is hereby incorporated byreference herein in its entirety. Scattering module 116 is used, amongother things, to determine the surface roughness of each semiconductorwafer 12 as it passes from wafer cassette 112 into process chamber 38.

To maintain load-lock chamber 110 and process chamber 38 under vacuum,load-lock chamber 110 also includes vacuum pump interface 118 whichpermits pumping package 122 to maintain vacuum. Process control computer126 controls the fabrication of semiconductor wafer in the reactor ofFIG. 5. Control signals from process control computer 126 includesignals to PID temperature/lamp power controller 136. PID controller 136provides various control signals to lamp module power supply 132. Lampmodule power supply 132, in turn, provides various control signals totungsten-halogen heating lamp module 134. Process control computer 126also directs control vacuum setpoints to pumping package 122 and gas andplasma inlet flow signals to gas distribution network 82. To provideproper activation of plasma species at discharge cavity 88, processcontrol computer 126 provides a control signal to microwave source 124which, in the preferred embodiment, operates at a frequency of 2450 MHz.

To control the input power of tungsten-halogen heating lamp module 134,process control computer 126 sends power control signals via line 138 toPID controller 136 in response to the temperature sensor outputs(received via line 140). Sensing lines 140 to process control computer126 from tungsten-halogen heating lamp module 134 include signals frommulti-point temperature sensor of the present invention which measurethe temperature of semiconductor wafer 22 in real time.

FIG. 6 is a schematic drawing illustrating a preferred embodiment oftemperature sensor of the present invention. In the discussions thatfollow, the detailed description refers to only one path for signalflow. In fact, the present invention may use numerous channels, and thepreferred embodiment has four paths for signal flow for four-pointtemperature measurements. Infrared CO laser 202 provides a coherentincident beam 203 to beam splitter module 204. Beam splitter module 204contains beam splitters S1 through S5 in the preferred embodiment whichsplit coherent incident beam 203 into five coherent beams withessentially equal intensities. For example, coherent beam 210 has equalintensity to all other beams split by beam splitter module 204. Infraredfiber connector 212 receives coherent beam 210 and sends it into fiber216. Remaining infrared laser energy from beam splitter S5 exits beamsplitter module 204 and is absorbed by absorber 208. From infrared fiberconnector 212 coherent beam 210 travels through optical fiber 216.Optical fiber 216 is used to measure an incident coherent beam powerlevel I. Optical fiber 214, however, leads directly to fiber bundle 218.Other types of beam splitters may be used instead of the design shown inFIG. 6.

Fiber-optic bundle 218 fits within bore 220 of lamp module 134. Fromfiber-optic bundle 218 incident coherent beam 224 is emitted throughoptical window 106. After traveling through optical window 106, incidentcoherent beam 224 is incident upon semiconductor wafer 22. A portion ofincident coherent beam 224 is reflected to become reflected coherentbeam 226. A portion of incident coherent beam 224 is transmitted throughwafer 22 to become transmitted coherent beams 228. Fiber-optictermination 230 receives transmitted coherent beam 228 which travelsthrough optical fiber 232 to become transmitted beam outputs T1.

The portion of incident coherent beam 224 that semiconductor wafer 22reflects is returned to fiber-optic bundles 218. Additionally, becauseof the elevated temperature to which lamp module 134 takes semiconductorwafer 22, semiconductor wafer 22 also emits incoherent radiant energy222. Fiber-optic bundle 218 receives reflected coherent beams andincoherent radiant energy and directs these signals to optical fibers227 to become received signals R1.

Sensor 200 of the present invention provides multi-point temperaturesensing of semiconductor wafer 22 with a real-time emissivitymeasurement. The real-time emissivity measurements are used forreal-time emissivity compensation and extraction of true wafertemperature. Infrared laser 202, in the preferred embodiment, comprisesa CO laser, however other forms of optical energy may be used to achievethe purposes of the present invention. Lamp module 134 comprises anarray of tungsten-halogen lamps used to heat the face-down semiconductorwafer 22. Lamp module 134 has a plurality of hollow light pipes designedto receive fiber-optic bundles 218. The typical diameter of bore 220ranges from 1/8" to 1/4", other diameters may be used, depending on thedesired dimension of each of the fiber-optic bundles 218 and othercharacteristics associated with lamp module 134 and semiconductor wafer22.

Optical vacuum window 106 separates lamp module 134 and fiber-opticbundles from semiconductor wafer 22. Additionally, optical window 106not only serves to transfer wafer heating flux and coherent laser energybetween wafer 22 and fiber-optic bundles 218, but also maintains acontrolled process environment or vacuum within the process chamber forprocessing semiconductor wafer 22. Optical window 106 is opticallytransparent for both the lamp energy from lamp module 134 and incidentcoherent laser beam 224 and reflected coherent beam 226. Opticaltransparency is a function of the window material and the wavelength ofthe optical energy passing through optical window 106 so the materialfor window 106 is selected with optical transparency in the desired bandas an essential criterion. For example, for 5.4 μm laser powertransmission, a window material such as sapphire or calcium fluoride maybe required. Smaller 5.4 μm transparent windows (e g., sapphire) may beproperty attached or sealed to a larger quartz window base plate.

As a further example, the points at which fiber-optic bundle 218 andother similar bundles transmit coherent laser beams through opticalwindow 106 can employ smaller view ports made of a material such assapphire, calcium fluoride, zinc selenide, barium fluoride, or someother suitable IR-transparent material. This may be desirable, becauseoptical transmission of thick (e.g., 0.5") quartz does not exceed 3.5μm, whereas the wavelength of the coherent infrared energy emitted fromfiber-optic bundle 218 may be approximately 5.4 μm, as in the preferredembodiment. Replacing sensor portions of optical vacuum quartz window106 that directly receive the output from fiber-optic bundle 218 andadditional similar bundles with a material transparent to infraredradiation assures that the infrared energy from fiber-optic bundle 218can transmit through optical window 106 and interact with semiconductorwafer 77.

Fiber-optic bundle 218 is positioned within lamp module 134 in order tominimize the direct lamp irradiation received by the bundle from thelamp module 134. As a result, the only signals that fiber-optic bundle218 receives from lamp module 134 are indirect reflected signals.Moreover, fiber-optic bundle 218 is designed to preferably transmit the5.4 μm wavelength energy from laser 82. At a wavelength of 5.4 μm, thereis negligible signal interference due to the heating lamps. This is dueto the fact that the quartz jackets of tungsten-halogen lamps cut offoptical radiation beyond 3.5-4 μm.

Although it is possible to operate infrared laser source 202 with aconstant output, in the preferred embodiment a chopped or modulatedoutput is used. Process control computer 126 controls chopping actionand frequency of infrared laser 202 to produce a low-frequency choppingof 5.4 μm wavelength coherent beam 203 into beam splitter module 204 inthe preferred embodiment. The laser chopping frequency is chosen to bemuch larger than the rate of real-time emissivity and temperaturemeasurements. The chopping frequently may be in the range of 100 Hz to10 KHz. Beam splitter module 204 divides the output of chopped infraredlaser 202 into n+1 channels, where n is the number of sensor points fortransmission and receipt of laser signals. The number of laser beamoutputs from beam splitter module 204 equals the number of points atwhich semiconductor wafer 22 is to be measured or, equivalently, thenumber of fiber-optic bundles 218, plus a reference output I. In thepreferred embodiment, n=4, so beam splitter module 204 splits outputbeam from laser 202 into 5 output beams having essentially equal outputpower or intensity levels.

Infrared laser 202 is a stable laser of known stable polarization andwithout mode hopping to provide a steady and known coherent infraredbeam output. Depending on the number of output beams from beam splittermodule 204, the split factor of beam splitters S1 through S5 may bedetermined. Thus, for example, if four sensing beams are to be splitfrom the output of infrared laser 202, beam splitters I through 5 wouldprovide an equal division in five levels to produce a reference signalI, and four beam outputs into fiber-optic bundles, such as fiber-opticbundle 218. The output laser beams may also have different intensitiesas long as the intensity ratios are known and remain constant.

Although the configuration of FIG. 6 illustrates sensing of fourdifferent points on semiconductor wafer 22, the application of thepresent invention can be extended to an arbitrarily large number, n, ofprobed points on the semiconductor wafer 12. For each number of points,n, beam splitter 204 would split the beam from infrared laser 202 inton+1 beams. The optimum number and positions of the sensing points dependon various factors including the heat source design (e.g., number oflamp heating zones) and wafer size.

Fiber-optic bundle 218, in addition to collecting reflected coherentbeams from semiconductor wafer 22, collects incoherent radiant energyemitted from semiconductor wafer 22. Fiber-optic bundle 218, therefore,receives a 5 KHz chopped reflected coherent beam 226 and a DC (or lowfrequency) radiant infrared energy emitted by wafer 22. As a result ofchopping the incident coherent beam 224 from infrared laser 202, it ispossible to identify and separate the AC component of the collectedsignal corresponding to the reflected coherent beam from semiconductorwafer 22 from the total signal that fiber-optic bundle 218 collects.This produces an AC signal component and a DC (or background lowfrequency) signal component of the collected signal that fiber-opticbundle 218 collects.

For low-temperature measurement applications, the preferred embodimentalso uses transmitted fiber termination 230 to receive that portion ofincident coherent beam 224 that transmits through semiconductor wafer22. In high temperature measurements (typically at least 600° C.) thesemiconductor wafer appears opaque to incident coherent beam 224. Thisis also true when the semiconductor substrate is heavily doped (P+ orN+). As a result, transmitted coherent beam 228 is insignificant forhigh temperature applications (e.g., temperature higher than 600° C).Additionally, if semiconductor wafer 22 contains significant amounts ofdoping in the substrate, the wafer will appear opaque to incidentcoherent beam 224 even at lower temperatures. In low-temperatureprocessing applications, however, incident coherent beam 224transmission through semiconductor wafer 22 may be significant. In suchcases, transmitted coherent beam 228 must be measured for precisereal-time emissivity measurements.

For each transmitted coherent laser beam 228 that passes throughsemiconductor wafer 22, fiber termination 230 receives the beam andtransmits it through infrared fiber cable 232 to the remainder of thesensor of the present invention.

FIG. 7 is a cross-sectional view of a time-division chopper multiplexerwith infrared fiber interface used in a preferred embodiment of thepresent invention. The signals I, R1 through R4, and T1 through T4 fromeach optical fiber, such as optical fiber 226, are received by fiberinterface chopper multiplexer 234. Fiber interface chopper multiplexer234 provides a time-division multiplexed optional signal 236 thatassociates with each of the fiber-optic cable input signals I, R1through R4, and T1 through T4. Infrared detector 240 receives thesesignals through detector window 238. Infrared detector 240 provides atime-division multiplexed electrical output signal 242 to other portionsof the closed-loop temperature controller on the fabrication reactor 80.

The preferred embodiment includes one cable 249 having a referenceoptical signal, one cable having an incident beam signal, I, four cableshaving reflected beam and collected radiance signals, R1 through R4, andfour cables having transmitted beam signals T1 through T4. Detector 240,in response to the power of the optical signal it receives, produces acurrent or voltage signal which is proportional to the signal power inthe respective optical channel.

Reference input channel 249 comprises the output of a semiconductordiode laser 446 (see FIG. 15) having frequency and/or amplitude valuesdiffering from those of I, R₁ through R₄, and T₁ through T₄, but stillwithin response range of detector 240. This allows process controlcomputer 126 to identify the beginning of each cycle of chopper wheel244 (see FIG. 8) for the purpose of synchronous operation. For example,output from semiconductor diode laser 446 for the reference signal 249may have a chopping frequency of 10 KHz. With this fundamentallydifferent chopping frequency, it would be clear to a process controlcomputer 126 that upon receiving signals from reference channel 249, anew cycle has begun (assuming that the infrared laser source 202 ischopped at a different frequency (e.g., 5 KHz). Other methods ofsynchronization are also possible.

Detector 240 includes a filter to block all but a prespecified bandwidtharound the spectral band associated with laser 202 wavelength of 5.4 μm,in the preferred embodiment. The bandwidth of optical filter, in thepreferred embodiment, may be 0.1 to 0.5 μm. It is important to centerthe bandwidth of the optical filter at the wavelength of infrared laser202.

It is possible to connect independent sensors to each of the fiber-opticcables that includes a transmitted or reflected signal fromsemiconductor wafer 22. It is also necessary to use a high-performancefast infrared sensor to measure the level of wafer radiance and infraredreflectance and transmittance for the semiconductor wafer at each probedpoint. To use multiple independent sensors for signal measurement,therefore, would not only be rather expensive for the purposes of thepresent invention, but also would unnecessarily create numerouscalibration requirements in relating the results of multiple detectors.However, multiple infrared detectors may be used instead oftime-division multiplexing with a single detector, if desired.

To overcome this problem, the present invention associates opticalfibers containing signals I, R₁ through R₄, and T₁ through T₄, forexample, with a single high-performance infrared detector. As a result,it is not necessary to check multiple detectors for signal drift andcalibration. Calibration of a single detector will maintain consistencyamong properly operating fiber- optic channels for multi-point waferemissivity and temperature measurements.

In the preferred embodiment of the present invention, infrared detector240 is a low-noise lead selenide (PbSe) or a mercury cadmium telluride(HgCdTe) detector unit that operates in the range of 77 to 200° K.(liquid nitrogen or thermoelectric-cooled). Other suitablehigh-performance low-noise sensors may also be used. Detector window 238is a thin plate of sapphire or calcium fluoride having an area ofbetween 2 and 5 mm² and is transparent to the infrared laser andreference laser beam. It is desirable to place the output of eachfiber-optic channel as close as possible to the detector window 238.

FIG. 8 is a cross-sectional side schematic view of the time-divisionchopper multiplexer with fiber interface illustrating the connection offiber-optic cables in a fiber-optic adapter module of a preferredembodiment. According to FIG. 8, each of the fiber-optic cablescontaining signals I, R₁ through R₄, T₁ through T₄, and REF (reference)fits through a channel 246 of fiber adapter module 248. Chopper wheel244 rotates at the frequency, f1, by being attached to shaft 250 whichcomputer- controlled stepper motor 252 drives. The chopper wheel 244permits time-division-multiplexed signals from fiber-optic cables 226 toreach detectors window 238. Detector element 239 converts infrared lightsignals from fiber-optic cables 226 into an electrical signal outputthat goes to the remainder of the sensor system 200 of the presentinvention.

Chopper wheel 244 scans each of the input optical channels at thefrequency, f1. The frequency, f1, is chosen depending on the choppingfrequency of infrared laser 202. For example, with a chopping frequencyof approximately 5 KHz, the scanning frequency f1 may be between 5 and50 Hz. Having f1 with a value of between 5 and 50 Hz in this instanceensures that the period of rotation of chopper wheel 244 is sufficientlylarge to assure many samples of each chopped input channel to reachdetector 240 (e.g., 10-100 samples or more) for proper signal timeaveraging.

Fiber adapter module 248 and chopper wheel 244 produce a rotatingscanning effect on each of the input optical channels: I, reference REF,R1 through R4, and T1 through T4.

Although there are numerous ways to configure chopper wheel 244 inmultiplexer 234, in the preferred embodiment the fiber adapter module248 places the input fiber-optic channels around the periphery with ashaft to support chopper wheel 244 at its center. Shaft 250 penetratesthrough fiber adapter module 248 through a collar 251 that permits freerotation of shaft 250. Shaft 250 connects to stepper motor 252 thatrotates, causing shaft 250 and chopper wheel 244 to rotate. Thefrequency of stepper motor 252 rotation may be controlled by processcontrol computer 126.

In order to maintain proper coupling between fiber adapter module 248and detector 240, fiber adapter module 248 is rigidly mounted todetector 240. Chopper wheel 244 rotates in the gap between the twofirmly attached components.

The angle, α, at which precision fiber channels of fiber adapter module248 reside is a function of the size of adapter module 248 and therelative position of the entering fiber lines to fiber adapter module248 and detector 240. Thus, as the number of input channels to fiberadapter module 248 increases, the angle α will decrease to accommodatethe greater diameter of fiber adapter module 248. Additionally, it isimportant not to have too small an angle, α, to prevent excessive beamdivergence and spread over detector window 238 and degrade the signalcollection from optical channels (246 through 211).

In the preferred embodiment of the present invention, the angle, α,approximates 45°. The ends of fiber-optic channels 211 through 246 donot include collimating lenses, but are polished to help minimizedivergence of the output laser signal. Because of the small distancebetween detector window 238 and optical channels 211 through 246, theabsence of a collimating lens only minimally affects the collection ofthe signals from the channels. However, collimating or beam-shapinglenses may be used at the fiber ends.

FIG. 9 shows a top down schematic view of the adapter module 248.Outputs from the adapter module 248 are spaced an equal distance nearthe periphery of the adapter module 248 having an equal angle, θ betweenadjacent output points.

FIG. 10 shows a top down prospective of chopper wheel 244. Chopper wheel244 is opaque except for slot 254 which is an arched opening extendingover an angle, θ, from its center. Chopper wheel 244 rotates aboveoutput side 222 of adapter module 248 to permit only one channel I, R1through R4, T1 through T4, or REF to transmit light signals to detector240. Within chopper wheel 244 appears a slot 254 whose edges 256 and 258form an angle from the center of chopper wheel 190, θ, which is smallerthan the angle created by the angle between adjacent fiber-opticchannels for example, through the center of fiber adapter module 192, φ,As chopper wheel 244 rotates from one input channel to the next, a briefperiod occurs when signal collection from fiber adapter module 248 isblocked. Although it is important to have this separation betweenadjacent signals, it is also important to minimize the differencebetween θ and φ so that the maximum amount of signal reception can occurat detector 240. It is desirable that chopper wheel 244 have as low amass as possible so that it may be rapidly controlled to vary speed andoperate at high speeds. To achieve these objectives, chopper wheel 244has a thickness of approximately 1 mm and a diameter of 5 to 20 mmcomprising material that is opaque to infrared laser emissions (e.g.thin stainless steel disk).

FIG. 11 is a representative time chart illustrating time-divisionchopping of semiconductor wafer reflectance, transmission and incoherentradiance signals for four-point measurements.

Reference input channel 249 provides a signal that identifies thebeginning of chopper wheel 244. As a result, a demultiplexer or othersignal identifier may associate with the output from detector 240 toidentify the beginning of each cycle of chopper wheel 244, andaccordingly identify each output from chopper wheel 244 into detector240.

For the transmitted fiber-optic terminations, there is a minimal levelof radiance collected from semiconductor wafer 22, but there may be alevel of transmitted coherent beams 228. In fact, for transmittedterminations 230, the parameter of greater interest is the 5 KHztransmitted laser beam signals. This reading would provide a value forthe semiconductor wafer transmittance at the infrared laser wavelength.

FIGS. 12a through 12e illustrate alternative embodiments of fiber-opticbundle 218 of the preferred embodiment. The preferred embodiment usesfiber-optic bundle 218 as described in FIG. 12a. Alternativeembodiments, such as those described in FIGS. 12b through 12f, may alsobe used. Fiber-optic bundle 218 has two primary purposes. The first ofwhich is to direct incident coherent beams to semiconductor wafer 22 andreceive reflective coherent beams from wafer 22. The second purpose isto collect the radiated black-body energy that semiconductor wafer 22generates.

Fiber-optic bundles 218 are designed so that they establish a channelfrom beam splitter module 204 through optical fiber 214 to the tip ofthe fiber-optic bundle 218. At the tip of fiber-optic bundle 218 appearsa collimating lens 312 to produce a collimated laser beam incident uponthe semiconductor wafer 22. Incidence of the coherent laser beam 224upon semiconductor wafer 22 produces a reflected component and atransmitted component (the transmitted component may be zero dependingon various factors).

The infrared laser 202 beam travels through optical fibers 214 tofiber-optic bundles 218 which are positioned within lamp module 134.From fiber-optic bundles 218 the incident coherent beams 224 shine onthe semiconductor wafer 22. Some of the light is reflected and some ofthe light is absorbed by the semiconductor wafer 22. Although it may bedesirable to use transmission measurements for numerous embodiments ofthe present invention, in the preferred embodiment only reflectance ismeasured. This provides a satisfactory measurement of the semiconductorwafer 22 emissivity, because at the thermal processing temperatures forwhich the present invention is employed, transmission of semiconductorwafer 22 is usually zero. By measuring the reflected coherent beam andwith knowledge of semiconductor wafer surface roughness, it is possibleto determine the amount of absorption or emissivity of the semiconductorwafer surface.

Fiber-optic bundles 218 use optical fibers comprising a fluoridecompound, however, chalcogenide may also be used. In the preferredembodiment of the present invention, the optical fibers 214 and 228 areof suitable material for the wavelength of infrared laser 202 ofapproximately 5.4 μm and may comprise materials such as chalcogenide,fluoride, or silver halide, or other suitably transparent transmittingmaterial for transmitting coherent light energy from beam splittermodule 204 to fiber-optic bundles 218. Fiber-optic bundle 218 of FIG.12a uses a 1/4" CaF₂ lens 312 with a single laser delivery fiber 214 andseveral return fibers 227 arrange to terminate in a plane parallel tolens 312.

Fiber-optic cables 214 and 227 in the present invention for bothtransmission and receipt are preferably multi-mode cables, becausemulti-mode fibers are easier to align and use for the application of thepresent invention. Delivery fiber 214 and return fibers 227 are movableto allow control of lens-to-bundle distance. Laser delivery fiber 214 isat the center line of fiber-optic bundle 218 and return fibers 227 arein the surrounding angular region. Lens 312 is anti-reflection coatedfor optimal transmission at a wavelength of 5.4 μm.

Transmitted coherent beam terminations 230 include collimating lens (notshown) to focus the transmitted coherent beams 228 into optical fibers232. The typical beam diameter emitted from infrared laser 82 is 2 to 3mm. Typically, as incident coherent beam 224 travels to and throughsemiconductor wafer 22 to become transmitted coherent beam 228,divergence of the laser beam occurs. Although it may change from laserto laser, the divergence of the laser beam passing through semiconductorwafer 22 is approximately 5 milliradians. Thus, as transmitted coherentbeam 228 reaches fiber-optic terminal collimating lens, its diameter mayapproach 4 to 6 mm. The collimating lens focuses the transmitted beam tothe fiber-optic core for transmission through fiber-optic cables 232.

Operation of fiber-optic bundle 218 is optimal for both emissivity andtemperature measurements. An emissivity measurement involves incidentcoherent beam 232 emitting from the tip of delivery fiber 214 with aknown half-cone angle of divergence (approximately 11°). Lens 312realigns incident coherent beam 224, depending on the relative positionof the optical fiber 214 tip to lens 312. Incident coherent beams 224leaving lens 312 arrive at semiconductor wafer 22. A portion of incidentcoherent beam 224 is reflected as reflected coherent beam 226 whichpasses back through lens 312 and is projected onto bundle tip 218.

The approximation of semiconductor wafer 22 as a partial specularreflector for reflected coherent beam 226 is acceptable at thewavelength of light considered in the present invention (i.e., 5.4 μm).The dimensions of the projected reflected image of delivery fiber 214depends on the relative distance between the tip of optical fiber 214and lens 312. This distance can be tuned to maximize the amount ofreflected coherent beam 226 that projects onto return fibers 227 insteadof projecting onto delivery fiber 214 and not being collected.

The bundle-to-lens distance has to be optimal to provide an acceptablelevel of light collected both by reflection and emission fromsemiconductor wafer 12. A basic limitation of the design of FIG. 12a isthat the return fibers 227 will collect not only the reflected coherentbeam and emitted radiant energy from the semiconductor wafer, but alsosome fraction of incident coherent beam will be reflected from lens 312back to return fibers 227 as well as reflected from the optical window106 separating the atmospheric ambient from the vacuum inside theprocess chamber. Although window reflection may be essentiallyeliminated by tilting optical window 106 at an appropriate angle to theincidental light direction, the lens reflection is not easilyeliminated. To overcome the limitation, the preferred embodimentutilizes a lens coating on lens 312 with an anti-reflection (AR) coatingspecific to the wavelength of infrared laser 202.

The fiber-optic bundle design of FIG. 12b is similar to that of 12a,except that lens 324 is smaller and serves as only a delivery path fordelivery fibers 320. The light path from semiconductor wafer 22 toreturn fibers 227, therefore, does not pass through lens 324. The designof fiber bundle 300 of FIG. 12b eliminates the direct reflection of lens324, but also causes a large area of the bundle at the criticalcollection location to be unavailable for collection of reflected laseror emitted wafer light. This is because lens 324 must be significantlylarger than the essential fiber diameter for proper collimation ofincident laser beam 224.

FIG. 12c provides yet another embodiment of fiber-optic bundle 302 thatuses a single large diameter fiber 328 to both deliver incident coherentbeams and collect reflected coherent beam and emitted wafer radiantenergy. In the fiber-optic bundle 302 of FIG. 12c, reflected coherentbeam 226 and emitted light 222 can be separated from incident coherentbeam 224 using either a beam splitter or a Brewster window arrangement.The design of FIG. 12c provides for collection of almost all of thereflected/emitted light focus by the lens, because the fiber can be madesufficiently large to accommodate a significant collection area. Thecollection area 334 is available for both incident and return beamtransmission. A disadvantage of the design of FIG. 12c, however,involves the direct reflection of incident coherent beam 224, not onlyat the lens surface but also at the entrance and exit from the fiber.Because the measured reflected power from semiconductor wafer 22 can beless than 50% of the incident power, this design may increase backgroundreflection to an unacceptable level.

The designs of FIGS. 12d and 12e may also be used as alternativeembodiments of the fiber-optic bundle. FIG. 12d shows a randomized arrayof delivery fibers 214 and return fibers 336 at the bundle 304. Thearrangement of FIG. 12d permits the system to be easier to align, butsuffers from the limitations of it not being clear what power level canbe driven into the laser bundle at the laser entry point. Withfiber-optic bundle 304, a significant portion of the beam power will beabsorbed by epoxy surrounding the fiber-optic cable and this may causedamage.

On the other hand, the configuration of FIG. 12e involves a single lightdelivery fiber 340 and a single return fiber 338. The two fibers arearranged at the sample tip, behind lens 312, such that the laser lightleaves the first fiber 340, goes through lens 312, and reflects atsemiconductor wafer 22. The beam is then refocused at the second fiber.The light emitted from semiconductor wafer 22 is also collected byreturn fiber 338. The limitation associated with the FIG. 12econfiguration is a critical dependance on precision alignment.

FIG. 13 is a cut-away side diagrammatic view of a cooling jacket 367used to maintain a low temperature at fiber-optic bundle 218 in thepreferred embodiment. Fiber-optic bundle 218 appears within sheath 368which serves as a water cooling shroud. Sheath 368 contains inlet 366and outlet 372. As fiber-optic bundle 218 increases in temperature asresult of its proximity to lamp module 134, it is important to maintaina constant and/or temperature in fiber-optic bundles 218. However, inorder to prohibit heat from lamp module 134 from adversely affecting thetransmission of coherent energy to and from fiber-optic bundles 218,cooling water 370 may be passed through inlet 366 into sheath 368 andthen exit the outlet 372. As water circulates through sheath 368, itremoves heat that lamp module 134 generates.

FIG. 14 is a partially cut-away perspective view of the presentinvention integrated with the process control computer of a rapidthermal processing system for the purpose of real-time semiconductorwafer fabrication process control. FIG. 15 is a schematic block diagramof the integrated system of FIG. 14. The output from detector 240 goesto demultiplexer 440. Demultiplexer 440 is programmed to recognize theorigin of the signal from detector 240 based on the reference signalfrom semiconductor diode laser 446. Demultiplexer 440 produces a signalon each line (total of 10 lines for this example) emanating fromdemultiplexer 440 and associated with each input fiber-optic cable thatleads into fiber-optic adapter module 234. Output from demultiplexer 440comprises analog electrical signals having a current or voltage levelrepresentative of various power channels received by detector 240. Theseanalog signals are converted to digital signals at analog-to-digitalconverter 442.

Output from analog-to-digital converter 442 goes to process controlcomputer 126. Process control computer 126 operates on digital inputfrom analog-to-digital converter 442 to further process the digitalsignals. Process control computer 126 digitally filters each of thedigital inputs to separate the AC and DC components of the receivedsignals, respectively representing the reflected coherent beam andradiance emitted from semiconductor wafer 22. Additionally, processcontrol computer 126 can determine reflectance and transmittance usingthe reflected and transmitted beam power levels to determinesemiconductor reflectance and transmittance. With these values, processcontrol computer 126 can determine semiconductor wafer 22 emissivity.

Having determined semiconductor reflectance, transmittance, radiance,and emissivity, process control computer 126 executes an algorithm todetermine the true semiconductor wafer 22 temperature in real-time. Thetemperature values that process control computer 126 determines are truetemperatures for each of the probe points associated with fiber-opticbundles 218.

Process control computer 126 may store, among other values, surfaceroughness for the particular semiconductor wafer being examined by thesensor of the present invention. Pending U.S. patent Ser. No. 638468entitled "Method and Apparatus for Semiconductor Wafer ProcessingDiagnosis and Prognosis" by Dr. Moslehi discloses a fiber-optic scattermodule or pre-process roughness sensor 116 for determining surfaceroughness of semiconductor wafer 22. The characteristics of that patentapplication are herein incorporated by reference and made part of thisapplication. In-situ measurement data from the scatter module 116 ofthat application may be stored in process control computer 126 and usedas part of the data necessary for accurate temperature measurement inthe present invention. Thus, in real time with each sampling of afiber-optic bundle 218 (i.e., during the period 1/f1) process controlcomputer 126 will provide a true temperature measurement for the pointon semiconductor wafer 22 associated with its respective fiber-opticbundle 218. In the preferred embodiment, these updates occur at every 20to 200 millisecond interval.

Actual emissivity of semiconductor wafer 22 may be taken by firstobtaining a value for the surface roughness of a semiconductor wafersuch as by using the scatter module 116 described in pending U.S. patentSer. No. 638468. The invention of that disclosure provides a value forboth coherent reflectance and scatter reflectance produced by thesurface roughness of the semiconductor wafer. Therefore if in theprocess chamber the coherent reflectance of the semiconductor wafer canbe measured using the sensor of the present invention, the relativeproportions of coherent reflected energy and scatter reflected energyobtained by scatter module 116 may be used to determine a real-timemeasurement for scatter reflection and total reflectance ofsemiconductor wafer for the incident coherent beams from fiber-opticbundles 218.

Process control computer 126 time averages the reflectance andtransmittance values over numerous to yield reliable time-averagedsemiconductor wafer 22 reflectance and transmittance values during thesemiconductor wafer 22 fabrication process. This produces time-averagedand noise-free reflectance, transmittance and emissivity values for thesemiconductor wafer. It is updated approximately every 20 to 200milliseconds. This updating rate falls within the required rate of lampcentral to accurately control a semiconductor wafer fabrication process.

With measured values for coherent reflectance and surface roughness ofsemiconductor wafer 22, it is possible to determine the totalreflectance of the semiconductor wafer, and likewise the totaltransmittance for the semiconductor wafer in real time. The totalreflectance and total transmittance values lead directly to emissivityvalues for the semiconductor wafer in real-time. Process controlcomputer 126 can be utilized to make these calculations at thewavelength of infrared laser 202 and in real time.

The measured signals received and manipulated by the process controlcomputer 126 may be compared to predetermined desired setpoints forsemiconductor wafer 22 temperature within the fabrication reactor. Forexample, assume a semiconductor wafer fabrication process is to occur at800° C. The sensor 200 utilizes fiber-optic bundles 218 and terminations230 to make measurements at four separate points on semiconductor wafer22. These measurements are used along with a real-time multi-zonecontroller to achieve the desired wafer temperature and to optimizeprocess uniformity. By associating a multi-zone lamp module 134 with atleast one fiber-optic bundle, it is possible to provide, through processcontrol computer 126, a feedback network that senses local temperatureat the sensing point at, for example, fiber-optic bundle 218 todetermine, in real time, whether the temperature of semiconductor wafer22 at that point satisfies the desired setpoint value. In the event thesetpoint value is not satisfied, the real-time PID controller willadjust the multi-zone lamp 134 power to cause semiconductor wafer toapproach the desired temperature of 800°, in the example.

The sensor 200 of the preferred embodiment has numerous applications andcan be used in numerous configurations of semiconductor wafer processingequipment. It allows real-time semiconductor wafer temperaturemeasurements and real-time adaptive uniformity control of semiconductorfabrication processes. No known systems for the semiconductor wafertemperature measurement can provide this type of real-time temperatureand uniformity control capability.

FIG. 16 illustrates an important relationship that exists between RMSsurface roughness and scattering parameter of a coherent laser beamincident upon the semiconductor wafer surface. It can be shown that thescatter reflective power P_(sr) and coherent reflected power P_(cr) of areflected laser beam varies as a function of a ratio of the RMS surfaceroughness of the semiconductor wafer and the wavelength of the incidentcoherent beam. The scattering parameter S_(r) is defined by thefollowing equation: ##EQU1## For given wavelength, W and scatteringparameter, S_(r), it is possible to determine the RMS surface roughness(for example, for wafer backsides).

FIG. 16 provides a calculated plot of this relationship for a laserwavelength W, of 1.3 μm and a laser wavelength of 1.55 μm. Along theordinate of FIG. 16 and ranging from 0.3 to 1.0 are values for thequantity 1-S_(r). Along the abscissa are the values of the dependentvariable, RMS surface roughness, ranging from 0 to 1,000 Å. An exampleof the use of FIG. 16 is as follows. Take, for example, the curveassociated with the laser beam having a wavelength of 1.3 μm and a valueof the scattering parameter 1-S_(r), of 0.79. The plot of FIG. 16provides an RMS roughness value of 500 indicated at point 452. Likewise,with the laser beam wavelength of 1.55 μm, the same scattering parametervalue 0.79 provides an RMS roughness value of 600 Å at point 450. Thecalculated chart of FIG. 16 shows that as the RMS roughness increasesfrom zero to 1000 Å, the scattering parameter S_(r) increases. Thiscauses 1-S_(r) to decrease to zero.

FIG. 17 is a diagram of calibration data relating the parameter,1-S_(r), obtained at a laser frequency of 1.3 μm to appropriate data ata laser wavelength of 5.4 μm. It can be shown that semiconductor wafersurface roughness does not change considerably with changes in wafertemperature. As a result, a measurement of incident coherent beamscattering at room temperature can, with minimal loss of accuracy, betaken as a measurement of semiconductor wafer scattering at the processtemperature. The scatter module 116 of pending U.S. patent applicationSer. No. 638468 measures incident beam coherent scattering at 1.3 μm.Infrared laser 202 produces an incident coherent beam having a 5.4 μmwavelength. The calculated plot of FIG. 17 relates scattering at 1.3 μmto beam scattering at 5.4 μm to provide an input value for scatteringparameter for process control computer 126 of the present invention.

FIG. 18 is a flow chart illustrating use of the integrated systemincorporating the preferred embodiment of the present invention togetherwith a process control computer for real-time semiconductor waferfabrication process control. The process begins at the start position of460. Once the process is started, the first step is to load asemiconductor wafer on the arm of the wafer handling robot at 462. Next,the wafer handling robot will move the semiconductor wafer to thescattering sensor and center the wafer at the scattering sensor at 464.The next step is to query whether the wafer is centered properly at thescattering center at 466. If the wafer is properly centered, then theprocess continues to the next step 468. Otherwise, the program returnsto step 464 to move the wafer to the center of scattering module 116(corresponding to optimum gap and tilt values).

The next step 468 in the process is to perform scattering measurementsat 1.3 μm. Next, using the Table of FIG. 18, process control computer126 extracts a scattering parameter at 5.4 μm at step 470. The next step472 is to load the wafer in the process chamber. The next step is toplace the semiconductor wafer against the lamp window at 474, and openthe shutter to the CO laser 202 at step 476. The next step in theprocess is to measure the DC detector voltage due to the wafer radianceat step 478. The process continues and computes the corresponding blackbody source temperature at actual radiance at step 480. Using theinfrared detector and process control computer of the present invention,the next step is to measure the incident, reflected, and transmitteddetector voltages from the chopped CO laser signal at step 482.

The next step is to compute wafer emissivity and temperaturecorresponding to the above radiance and laser signals in scattering intosolution at step 484. Once this is done, the next step 486 is to reportthe temperature to lamp controller portion of process computer 126. Thenthe program queries whether wafer processing is done at 488. If not, theprogram returns to step 482 and proceeds to measure incident, reflected,transmitted detector voltages from chopped CO laser signals. Thisprocess will continue to the "done processing"? query at 488 until infact processing is finished. Once processing is done the process entailssending a signal to close the laser shutter at 490. The next step is totake the wafer out of process chamber 38 using wafer handling robot atstep 492, and put semiconductor wafer 22 in its handling cassette atstep 494. If more wafers are to be processed then, in response to thequery at 496, program control returns to step 462 where yet anotherwafer is loaded on robot. Otherwise, the algorithm ends at step 498 andprocessing is complete.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

What is claimed is:
 1. A real-time, non-invasive, in-situ sensor fortemperature measurement of a heated semiconductor wafer, comprising:anelectromagnetic energy source for directing a plurality of incidentcoherent beams of elecromagnetic energy to selected areas of the surfaceof the semiconductor wafer; apparatus for collecting a plurality ofreflected beams of electromagnetic energy resulting from the reflectionof said plurality of incident coherent beams from the semiconductorwafer; apparatus for collecting incoherent radiant energy emitted from aplurality of points on a heated semiconductor wafer; a detector formeasuring one of said incident coherent beams of electromagnetic energy,said reflected beams of electromagnetic energy, and said incoherentradiant energy; apparatus for coupling said incident coherent beams ofelectromagnetic energy, said reflected beams of electromagnetic energyand said incoherent radiant energy to said detector, and circuitryconnected to said detector for calculating temperature values for thesemiconductor wafer as a function of said plurality of incident andreflected coherent beams and said incoherent radiant energy.
 2. Theapparatus of claim 1, further comprising circuitry for associating eachof said plurality of incident coherent beams with a corresponding one ofthe reflected coherent beams, and further associating each incidentcoherent beam and said corresponding reflected coherent beam with theincoherent radiant energy collected from the probed point of thesemiconductor wafer to yield a temperature value for each respectiveprobed point of the semiconductor wafer.
 3. The apparatus of claim 2,wherein the semiconductor wafer resides within a semiconductor waferfabrication reactor comprising a multi-zone lamp module and forindependently and directly heating predetermined regions of thesemiconductor wafer.
 4. The apparatus of claim 3, further comprisingcircuitry for associating each of said zone temperature values with atleast one of said predetermined regions, and controlling said multi-zonelamp module in response to said associated temperature values.
 5. Theapparatus of claim 4, further comprising circuitry for calculating theemissivity for at least one of said incidence and reflection pointssimultaneous with calculating the incoherent wafer radiance andtemperature values associated with each of said incidents and reflectionpoints on the semiconductor wafer.
 6. The apparatus in claim 1, whereinthe semiconductor wafer resides within a semiconductor wafer fabricationreactor having a wafer heating lamp module for directly heating thesemiconductor wafer and wherein said incident coherent beam collectingcircuitry and said reflected coherent beam and incoherent radiant energycollecting circuitry operate in real time as said heating lamp moduleheats the semiconductor wafer.
 7. The apparatus of claim 6, wherein saidincident and reflected coherent beam circuitry respectively direct andcollect said incident and reflected beams and said incoherent radiantenergy collecting circuitry collects said radiant energy along adirection approximately perpendicular to the semiconductor wafer.
 8. Theapparatus of claim 1, further comprising circuitry for calculatingemissivity of the semiconductor wafer as a function of said incidentcoherent beam energy and reflected coherent beam energy.
 9. Theapparatus of claim 1 wherein said incident coherent beams ofelectromagnetic energy are in the infrared spectral band.
 10. A methodfor real-time, non-invasive, in-situ temperature measurement of a heatedsemiconductor wafer comprising the steps of:directing a plurality ofincident coherent beams of optical energy to selected areas of thesurface of the semiconductor wafer; collecting a plurality of reflectedcoherent beams of optical energy resulting from the reflection of saidplurality of incident coherent beams from the semiconductor wafer;collecting incoherent radiant energy emitted from a plurality of regionson a semiconductor wafer; transmitting one of aid incident coherentbeams of optical energy, said reflected coherent beams of optical energyand said incoherent radiant energy to a detector; detecting the presenceof incident coherent beams of optical energy, reflected coherent beamsof optical energy and incoherent radiant energy; and calculatingtemperature values for the semiconductor wafer as a function of saidplurality of incident and reflected coherent beams and said incoherentradiant energy.
 11. The method of claim 10, further comprising the stepof associating each of said plurality of incident coherent beams with acorresponding reflected coherent beam, and further associating eachincident coherent beam and said corresponding relfected coherent beamswith the incoherent radiant energy collected from the point of incidenceand reflection from the semiconductor wafer to yield a temperature valuefor each respective probed point of the semiconductor wafer.
 12. Themethod of claim 11, wherein the semiconductor wafer resides within asemiconductor wafer fabrication reactor comprising a multi-zone lampmodule and further comprising the step of independently and directlyheating predetermined regions of the semiconductor wafer.
 13. The methodof claim 12, further comprising the step of associating each of saidpoint temperature values with at least one of said predeterminedregions, and controlling said lamp zones in response to sad associatedtemperature values.
 14. The method of claim 10, wherein thesemiconductor wafer resides within a semiconductor wafer fabricationreactor having a heating lamp module and further comprising the step ofdirectly heating the semiconductor wafer using said lamp module.
 15. Themethod in claim 14, wherein said incident coherent beam directing stepand said reflected coherent beam and incoherent radiant energycollecting steps take place in real time as said lamp module heats thesemiconductor wafer.
 16. The method of claim 14, wherein said incidentand reflected coherent beams are, respectively, directed and collectedand said incoherent radiant energy is collected at a point on the waferand along a path approximately perpendicular to the semiconductor wafersurface.
 17. The method of claim 14, further comprising the steps ofcalculating the emissivity of each of said incidence and reflectionpoints simultaneous with calculating the temperature values associatedwith each of said incidence and reflection points.
 18. The method ofclaim 10, further comprising the step of calculating emissivity of thesemiconductor wafer as a function of said incident coherent beam opticalenergy and reflected coherent beam optical energy.
 19. The method ofclaim 10, further comprising the steps of:measuring the surfaceroughness of the semiconductor wafers; and calculating a temperaturevalue for the semiconductor wafer as a function of said plurality ofincident and reflective coherent beams, said incoherent radiant energy,and said surface roughness.